As known, internal combustion engines generate mechanical power by extracting energy from heat flows. Engines are inefficient, so more heat energy enters the engine than comes out as mechanical power. The difference is waste heat, which must be removed. Internal combustion engines remove waste heat through cool intake air, hot exhaust gases, and explicit engine cooling. Cooling is also needed because high temperatures damage engine materials and lubricants. Internal-combustion engines burn fuel hotter than the melting temperature of engine materials, and hot enough to set fire to lubricants.
Engine cooling removes energy fast enough to keep temperatures low so the engine can survive. Most internal combustion engines are fluid cooled using a liquid coolant run through a heat exchanger (radiator) cooled by air. Liquid-cooled engines usually have a circulation pump.
Modern internal combustion engines use a split cooling system, which features separate circuits for the head and cylinder block, enabling faster warm-up. In particular, during warm up the split cooling layout can allow to cool at first the cylinder head alone and only after a given time interval the cylinder block too. The reason is that the cylinder head has a lower mass than the engine block and is exposed at very high temperature. Therefore, the cylinder head becomes warmer than the cylinder block and needs to be cooled earlier. Some advantages are reached, by means of such split cooling system: oil optimum temperature, better combustion conditions, faster warm up, reduced specific consumption and emissions.
Moreover, recent studies and product developments have shown that there is a significant potential to be tapped by using a cylinder head integrated exhaust manifold with turbo charged engines. It offers a win-win employment of technology providing improvements in the relevant attributes as well as a cost reduction, in particular, achieving better fuel economy while reducing emissions. With the catalytic converter closer to the engine exhaust point, the emissions reduction process begins sooner, resulting in lower emissions. Due to less surface area, such solution also contributes to a reduction in engine noise at idle.
On the other hand, split cooling system for internal combustion engines having an integrated exhaust manifold are not suitable for such engines that needs fast temperature warm-up for the exhaust line, as Diesel engines. For such engines is very important to reach as fast as possible the so called light-off temperature, i.e. the temperature at which catalytic reactions are initiated within a catalytic converter.
Therefore a need exists for a new split cooling system which is suitable for engine architectures foreseeing an integrated exhaust manifold.